This application claims priority under 35 U.S.C.xc2xa7xc2xa7119 and/or 365 to 99100584.4 filed in Europe on Jan. 14, 1999; the entire content of which is hereby incorporated by reference.
The present invention relates to routing and alternative routing in a telephone network or similar networks comprising several nodes. More specifically, the invention relates to improvements providing additional possibilities for alternative routing when experiencing congestion and avoiding circular routing.
It is known to provide nodes in such networks with alternative routing possibilities using alternative routing schemes like automatic alternative routing, automatic re-routing, load sharing and event dependent routing (CCITT recommandations, E.170). Circular routing is usually prevented by restricting the possibilities for using the alternative routing schemes, or, in more complex solutions, by detecting and eliminating loops in the routing performed (EP 550,180). The mentioned restrictions are usually provided by permitting alternative routing dependent on certain received parameters indicating the type and position of the congestion leading to the need for using alternative routing. This will often lead to release of calls which could be routed through to the destination.
It is an object of the invention to provide an improved alternative routing of calls in networks, said improvements preferably comprising the possibility of using alternative routing in accordance with several different routing schemes in a node and preventing circular routing by limiting the number of times a certain routing shceme is permitted for each call set-up. This is made possible by providing the call signalling with supplementary indicators indicating the types of alternative routing performed in preceding nodes. By appropriate use of these indicators it is achieved that the alternative routing of the calls may be performed less restrictive without increased risk of circular routing. The supplementary indicators make it possible to perform alternative routing for a call in a node in a situation in which the normal procedure would release the call due to the risk of circular routing.